Ha ha. Very funny. (It’s tax day in the US, for you foreign readers.) Thanks once again to Skaði Nordic for sponsoring this week in review:

A twopart series examining the question of ‘home snow advantage’. The short answer is that while overall there is generally no (statistically) significant effect, there are noticeable differences between athletes and nations that are quite interesting.

A look back at the career of a great Italian sprinter who’s retiring this season, including some interesting stats that place her as one of the most consistent sprinters ever.

Gee, I wonder what the bignews in XC skiing this week could be? It sounds from the translated reports from Norway and Estonia that I’ve read that Andrus Veerpalu tested positive (both A and B samples) for human growth hormone, but is denying any wrongdoing. Naturally, this means I started the week off with:

A new post revisiting my older one on Veerpalu. A common accusation against Veerpalu (and other suspected dopers) is that they have an unusual ability to show up at major events and ski much faster than they “normally” do. What I hope people take away from these two posts is that (a) our intuitive sense for “unusual” results does not always match the data, and (b) the answer you get will depend strongly on how you measure performance. The resulting situation is pretty ambiguous, which is why I would never recommend this line of reasoning as a serious accusation against someone.

The first of several posts looking back at the careers of skiers who have decided to retire. This week was Pirjo Muranen’s turn.

Finally, I’m going to take this opportunity expand briefly on something I tweetedabout. I read that one of the statements made at Veerpalu’s press conference in his defense was that he had passed more than 100 drug tests in the past. Although sports fans are becoming more educated about the statistics of drug testing, some confusion still remains. Without getting into the technical details, here’s the basic story.

Drug tests can make two types of mistakes: false positives, where we incorrectly label a clean athlete as a doper, and false negatives, where we incorrectly label a doped athlete as clean. In general, any testing scheme will involve a trade-off between these two types of errors. If you tweak your methodology in order to reduce the number of false positives, you will inevitably increase the number of false negatives. This trade-off cannot be outwitted! I often hear people suggest that maybe if we combine two, or three tests, or engage in some other complicated scheme, that you can reduce both types of error at the same time. Some testing procedures will be better than others in terms of both types of error, but whatever complicated combination of procedures and tests you invent, the end result will always amount to a single, big test that is itself subject to this very trade-off.

Drug testing in sports, for obvious reasons, is often calibrated in a such a way that false positives are considered far worse than false negatives. Specifically, tests are often constructed in order to be very careful to avoid falsely accusing an athlete of doping. Sadly, this means that negative results are simply less informative, in that they are much less likely to actually mean the person is clean.

My general conclusion as a stat guy is that I’m much more likely to believe that a single positive result is accurate than I am a single (or even many) negative results. A string of negative results doesn’t receive zero weight in my book, but they don’t receive much. (This is ignoring extra-statistical issues like mishandling samples at the lab, corrupt labs, or other similar human factors.)

Finally, having exhausted the list of retiring cross-country skiers, we’ve moved on to biathletes, beginning with Germany’s Martina Beck.

I talked some friends into doing their first trail running race this weekend, so I’m looking forward to a nice 20 mile run in Montana’s Bridger mountains tomorrow. Hopefully we’ll all still be friends on Sunday…

FasterSkier published a short piece of mine looking at what happens to skiers who’ve performed at different levels at World Juniors or U23s, and I followed that up with similar graphs for Canada and Germany (and more to come!).

Finally, we’re nearing the end of the list of retiring skiers, this week learning about the career of Milan Sperl.